Conventionally known apparatuses that observe magnetic domains and display their images include magnetic-field observing apparatuses utilizing a magnetic Kerr effect, scanning electron microscopes (spin polarized SEM), and transmission electron microscopes. However, these apparatuses can simply display images of magnetic domains but are not adapted to also display an image of distribution of coersive forces in magnetic domains.
The magnetic-field observing apparatus utilizing the Kerr effect measures coersive forces utilizing the fact that allowing a linearly polarized light beam to impinge on a magnetized recording medium rotates a plane of polarization of the light beam depending on a magnetic field. However, it is difficult for the magnetic-field observing apparatus utilizing the Kerr effect to condense the light beam until its beam spot size becomes of the order of nanometers. Thus, this observing apparatus does not enable magnetic domains to be observed at a nano-scale resolution. This prevents the nano-scale distribution of coersive forces from being determined.
Further, for the observation of magnetic fields, the electron microscope offers as high a resolution as that offered by the magnetic-force microscope. However, the electron microscope basically does not enable measurements in magnetic fields. Accordingly, to determine the distribution of coersive forces, it is necessary to take out a sample for each applied magnetic field to magnetize the sample and insert the sample into a measuring instrument again for measurements. This disadvantageously makes it impossible to measure the sample while directly viewing flux reversal at the same position of the sample to determine the nano-scale distribution of coersive forces.
The magnetic-force microscope (MFM) is known to detect the distribution of magnetism on the surface of the sample and display an image of the distribution as disclosed in, for example, J. Appl. Phys. 70(4), 15 Aug. 1991, P2413-2422, H. W. van Kesteren or Jpn. Pat. Appln. KOKAI Publication No. 2003-344258. The magnetic-force microscope enables magnetic domain structures to be observed on a nano-scale. The magnetic-force microscope (MFM) is known as an apparatus having a magnetic probe at a tip of a cantilever and which utilizes the fact that the magnetic probe is slightly displaced according to the distribution of the magnetism on the sample surface to display an image of the slight displacement to provide an image corresponding to magnetic domains on the sample surface.
In the field of magnetic recording, very high density recording at 400 Gbit/inch2 is generally strongly desired to be achieved within the next 10 years. As a recording scheme for achieving such recording, perpendicular magnetic recording has been energetically studied. Implementation of perpendicular magnetic recording requires a perpendicular magnetic recording medium to be developed which has an easy axis of magnetization in a direction perpendicular to a surface of a recording medium. Further, for implementation of very high density recoding, a reduction in noise in the recording medium is important.
To eliminate the cause of the medium noise, the magnetic domain structure in the medium needs to be precisely controlled. Accordingly, it is essential to clarify the nano-scale distribution of coersive forces in the medium.
The resolution of the magnetic-force microscope (MFM) has already reached a value of 20 nm or less. Further, the magnetic-force microscope can be used to produce and observe samples more easily than the above other techniques for observing magnetic domains. The magnetic-force microscope is thus suitable not only for basic researches but also for developments and researches that require a large number of test samples to be statistically processed. The magnetic-force microscope is actually used for a wide range of material developments including evaluations of magnetic recording media and recording heads, observations of magnetic domains on nano-scale thin films, and observations of magnetic vortices in superconductive materials. However, most of the researches using the conventional magnetic-force microscope are limited to observations of magnetic domain structures. In particular, observations of magnetic domains in magnetic fields are limited to relatively low magnetic fields of at most several kOe.
The magnetic-force microscope (MFM) is a preferable apparatus for displaying an image of the magnetic domain structure of such a perpendicular magnetic recording medium (magnetic thin film). However, the magnetic-force microscope only displays an image of intensities of magnetic fields in magnetic domains. No considerations are given for the additional display of nano-scale distribution of coersive forces. If the nano-scale distribution of coersive forces in the magnetic domain structure can also be displayed, it is expected to be possible to precisely control the magnetic domain structure in the perpendicular magnetic recording medium. This is expected to allow perpendicular recording media with reduced noise to be successfully developed.
Further, to examine a magnetic reversal process that is a process of writing information to a pattern medium, it is desirable to continuously or stroboscopically observe a variation in the magnetic domain structure at the same position of a sample to which a large magnetic field of several kOe is applied.